Effects of NO3 (-) and PO4 (3-) on the release of geogenic arsenic and antimony in agricultural wetland soil: a field and laboratory approach.

The dynamics of arsenic (As) and antimony (Sb) in wetland soil periodically submitted to agricultural pressure as well as the impact of soil enrichment with NO3 (-) (50 mg L(-1)) and PO4 (3-) (20 mg L(-1)) on As and Sb release were evaluated at both field and laboratory scales. The results showed that As and Sb exhibited different temporal behaviors, depending on the study scale. At field scale, As release (up to 93 μg L(-1)) occurred under Fe-reducing conditions, whereas Sb release was favored under oxidizing conditions (up to 5 μg L(-1)) and particularity when dissolved organic carbon (DOC) increased in soil pore water (up to 92.8 mg L(-1)). At laboratory scale, As and Sb release was much higher under reducing conditions (up to 138 and 1 μg L(-1), respectively) compared to oxic conditions (up to 6 and 0.5 μg L(-1), respectively) and was enhanced by NO3 (-) and PO4 (3-) addition (increased by a factor of 2.3 for As and 1.6 for Sb). The higher release of As and Sb in the enriched reduced soil compared to the non-enriched soil was probably induced by the combined effect of PO4 (3-) and HCO3 (-) which compete for the same binding sites of soil surfaces. Modeling results using Visual Minteq were in accordance with experimental results regarding As but failed in simulating the effects of PO4 (3-) and HCO3 (-) on Sb release.